Mass spectrometry is a widely accepted analytical technique for the accurate determination of molecular weights, the identification of chemical structures, the determination of the composition of mixtures and quantitative elemental analysis. It can accurately determine the molecular weights of organic molecules and determine the structure of the organic molecules based on the fragmentation pattern of the ions formed when the molecule is ionized.
Mass spectrometry relies on the production of ionized fragments from a material sample and subsequent quantification of the fragments based on mass and charge. Typically, positive or negative ions are produced from the sample and accelerated to form an ion beam. Differing mass fractions within the beam are then selected using a mass analyzer, such as single-focusing or double-focusing magnetic mass analyzer, a time-of-flight mass analyzer, a quadrupole mass analyzer, or the like. A spectrum of fragments having different masses can then be produced, and the compound(s) within the material sample identified based on the spectrum.
An improved form of mass spectrometry, referred to as tandem mass spectrometry or MS/MS has been developed where a mass-selected ion beam (referred to as the parent ion stream) produced by a first mass analyzer is dissociated into a plurality of daughter ion fragments. The daughter ion fragments are then subjected to a second stage of mass analysis, allowing mass quantification of the various daughter ion fractions. Such tandem mass spectrometry has been found to provide much more information on the material being analyzed and to allow for improved discrimination between various species that may be present in a particular sample.
In combination with "soft" ionization techniques, MS/MS can be a powerful characterization method for mixtures, separating individual molecular ions, and obtaining structural information by dissociating each followed by product ion mass analysis. New ionization methods, such as matrix assisted laser desorption are capable of producing singly charged ions from biomolecules in the 100,000 molecular weight range. However, collisionally activated dissociation (CAD), the most widely used method of MS/MS is ineffective at breaking apart singly charged ions with m/z&gt;3000. Using surface collisions in hybrid instruments, it has been demonstrated that high internal energy can be deposited into small ions, with internal energy deposition controlled by varying the collision energy. Bier et al., Int. J. Mass Spectrom. Ion Proc., 1987, 31-47, and references cited therein. Such high internal energy deposition shows promise for promoting structurally useful dissociations in large ions. For extending these measurements to large biomolecules, time-of-flight (TOF) mass spectrometry has the advantages of virtually unlimited mass range and multichannel detection.